Semiconductor devices such as diodes and transistors develop their functions by junction between semiconductors which exhibit different types of conductivity. Examples of the junction include pn junction and pin junction. These semiconductors have been produced by using metalloid elements such as silicon and germanium. Since these materials have high production cost and readily deteriorate at a high temperature, they are not always satisfactory as semiconductor materials used for industrial purposes.
Metals and conductive oxides are widely used as conductive materials constituting electrodes and wirings in various electronic devices. Films made of these metals and conductive oxides have been formed by a gas-phase process such as sputtering, laser ablation or vapor deposition. However, as the gas-phase process requires a giant expensive apparatus and has low film productivity, costs required for film formation become a great burden. Especially when a metal film is to be formed on a substrate by this process, the substrate must be heated at a high temperature in order to convert a precursor compound into a metal on the substrate. Therefore, the application of this process to, for example, a resin substrate having low heat resistance or a substrate after an electronic device which is destroyed at a high temperature is formed thereon is limited.
Further, when a conductive material is to be formed by the gas-phase process, a simple film formation method such as a printing method cannot be employed. To form a conductive film by the printing method, a liquid-phase process must be developed.
Then, a technology for forming a metal film and a conductive oxide film by an inexpensive liquid-phase process has recently been studied and reported. For example, JP-A 2009-227864 discloses a technology for forming an aluminum film on a substrate by applying a composition containing an alan-amine complex to a substrate and heating it at about 200° C. This is an excellent technology capable of forming a metal film on a substrate at a relatively low temperature by the liquid-phase process. However, there is demand for the further reduction of the ultimate temperature of the substrate. C. K. Chen, et al., Journal of Display Technology, Vol. 5, No. 12, pp. 509-514 (2009) disclose a technology for forming an IZO (Indium Zinc Oxide) film by applying a composition solution containing indium chloride and zinc chloride as a precursor to a substrate and heating it. However, a film obtained by this technology is unsatisfactory in terms of conductivity and is not put to practical use yet.
Although there are some reports about film formation by the gas-phase process in the prior art as for p-type semiconductors, the formation of a p-type semiconductor film by the liquid-phase process does not succeed yet.